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New Power for Hybrid Automobiles

Finalist for European Inventor of the Year 2009 in the “Non-European” category

Until
the mid 1990s, lack of battery performance stalled the commercial use of hybrid
cars. Things changed with the introduction of a new breed of power-management
system, developed by Japanese engineer Shoichi Sasaki for Toyota's hybrid
automobiles in 1997. Millions of hybrid vehicles have been sold today.

At a glance

Inventor: Shoichi Sasaki (JP)

Invention: Power control system for hybrid automobile

Sector: Automotive

Company: Toyota

An environment-friendly technology, hybrid
automobiles combine "regular" combustion engines with electrical drives. Today,
their owners enjoy tax benefits and low fuel consumption. But for a long time,
the technology suffered from a crucial fault. The rechargeable batteries lost
their ability to charge fully after periods of extended use.

In 1994, a development team led by engineer Shoichi
Sasaki at Toyota in Japan received the assignment to
perfect the technology. They reviewed over 100 designs for hybrid vehicles and
researched battery technology extensively.

Sasaki's discovery: Batteries reach their
optimal life span when kept at a constant state of charge (SOC) between 40 and
60% of their full capacity. Overcharging the battery leads to "aging" effects
similar to those common in laptop computers.

Based on this finding, Sasaki created a new
power management system that constantly monitors battery charge in a hybrid
vehicle. It controls power supply to the battery and levels discharge to
maintain the optimal state of charge.

The battery is charged by motor generators
while driving, or by energy released during braking. Discharge happens when the
car's electric drive takes over, mainly in city traffic - a driving environment
featuring (fuel-intensive) stop-and-go patterns.

The new power-control system developed by Japanese inventor Shoichi Sasaki ensures a long life for batteries in hybrid cars. The invention paved the way for the next generation of hybrid vehicles based on the step-up voltage concept. The concept allows for compact battery size with improved driving performance.

Numerous other brands have
also introduced hybrid vehicles, and many companies and governments offer
benefits for purchasing hybrids. By 2008, Toyota
had already sold more than 1 million "Prius" automobiles worldwide.